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Measuring Physical Properties at the Surface of a Comet Nucleus

By Andrew J. Ball


The European Space Agency’s cornerstone mission Rosetta is due for launch in\ud January 2003. It will perform a rendezvous with comet 46P/Wirtanen beyond 3 AU and,\ud following an initial mapping phase, deploy a lander to a selected site on the nucleus\ud surface. The Rosetta Lander will provide unprecedented access to cometary material.\ud Some of the most uncertain characteristics of the nucleus material are physical properties\ud such as its density, the structure of the surface layers and its mechanical strength.\ud MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) is one of the\ud experiment packages selected for the Lander payload which will address certain physical\ud properties and their evolution with time. This thesis focuses on the in situ measurement of\ud the density of the surface layers by a radiation densitometer incorporated into the MUPUS\ud thermal probe, and on the penetrometry measurements to be performed by an\ud accelerometer mounted in the Lander’s anchoring harpoon.\ud A concept for incorporation of a gamma ray attenuation densitometer into the\ud thermal probe is presented and explored. A 137Cs radioisotope source will be mounted near\ud the tip of the probe and semiconductor radiation detectors situated at the top of the probe\ud will monitor the transmitted count rate during probe insertion, as the intervening material\ud attenuates the radiation. Preliminary experiments to evaluate cadmium telluride (CdTe)\ud detectors for this purpose are presented, as well as results from a specially-developed\ud Monte Carlo computer code designed to model the absorption and scattering of photons in\ud bulk material.\ud Also presented is a control algorithm to dynamically re-budget the integration time\ud and depth resolution of the instrument as it is inserted by the hammering mechanism. This\ud is required due to: a) the wide range of possible densities the instrument may encounter, b)\ud the variation vs. depth of required integration time, and c) the limited time in which the\ud measurement must be performed. For lower than nominal densities, integration time may\ud be wasted when it could be used to improve the accuracy and depth resolution. For higher\ud densities the integration time at particular depths may not be sufficient to obtain acceptable\ud accuracy; in this case some depth resolution could be sacrificed to improve the accuracy.\ud The proposed algorithm uses the density measured at each point to update the time budget\ud and depth resolution for the remaining stages of penetration.\ud Although the use of the gamma ray backscatter type of densitometer was eventually\ud rejected in favour of the aforementioned attenuation technique, investigation of the\ud backscatter technique resulted in an extension to the Single Scattering Model– an analytic\ud approximation of its operation. This extended model adds to our understanding of these\ud devices' response to spatial inhomogeneity.\ud Calculations show that anchoring of the Lander is necessary to avoid possible\ud ejection from the nucleus by gas drag in the case of a landing in an active area. The use of\ud the Lander’s anchoring harpoon to perform penetrometry measurements is reported,\ud including the results of preliminary experiments and techniques for analysing the\ud accelerometry data. It is shown that layers with distinctly different strengths may be\ud identified, and that the mean deviatoric stress– a strength parameter– may be constrained to\ud within a factor of about 2.2. This would be a significant improvement on current estimates,\ud which vary by several orders of magnitude.\ud Together with other investigations on the Rosetta mission the densitometry and\ud penetrometry measurements will serve to constrain models of the physical state and\ud evolution of the cometary material found at the landing site. In particular both instruments\ud are sensitive to near-surface layering, which may be expected from theoretical models of\ud cometary activity

Topics: QB
OAI identifier: oai:kar.kent.ac.uk:23088

Suggested articles



  1. (1976). (in Russian). Translation in Cosmic Res.
  2. (1951). A Comet Model I. Physical Relations for Comets and Meteors. doi
  3. (1950). A Comet Model I. The Acceleration of Comet Encke. doi
  4. (1997). A New Method for the Determination of Thermal Conductivity and Thermal Diffusivity from Linear Heat Source Measurements. doi
  5. (1983). Advances in Gamma-Gamma Logging. doi
  6. (1989). Agency, doi
  7. (1986). Agency, Comet Nucleus Sample Return. doi
  8. (2000). Agency, European Space Science Horizon doi
  9. (1993). Agency, Rosetta Comet Rendezvous Mission, doi
  10. (1991). Agency, Rosetta Comet-Nucleus Sample Return: Mission and System Definition Document.
  11. (1987). Agency. Rosetta Comet Nucleus Sample Return: Report of the Science Definition Team.
  12. (1971). An Air Dropped Sea Ice Penetrometer.
  13. (1983). An Assessment of Existing Klein-Nishina Monte Carlo Sampling Methods.
  14. (1984). An Idealized Short-Period Comet Model: Surface Insolation, H2O-Flux, Dust Flux, and Mantle Evolution. doi
  15. (1994). An Impact Penetrometer for a Landing Spacecraft. doi
  16. (1996). Analysis of Vertical Projectile Penetration in Granular Soils. doi
  17. (1995). Announcement of Opportunity for RoLand Surface Science Instruments. RoLand consortium,
  18. (1974). Apollo Soil Mechanics Experiment doi
  19. (1995). Application of an Efficient Materials Perturbation Technique to Monte-Carlo Photon Transport Calculations in Borehole Logging. doi
  20. (1995). Bulk Density of Asteroid 243 Ida from the Orbit of its Satellite Dactyl. doi
  21. (1991). CO2-Profiles in Cometary Analogs. In: Solid State Astrophysics
  22. (1989). Collisions of Macroscopic Fluffy Aggregates in the Primordial Solar Nebula and the Formation of Planetesimals.
  23. (1996). Comet 46 P/Wirtanen Nucleus Reference Model.
  24. (1995). Cometary Activity and Nucleus Models. doi
  25. (1995). Cometary Ice Texture and the Thermal Evolution of Comets. doi
  26. (1995). Cometary Lander for the Rosetta Mission. Proposal to ESA. RoLand consortium,
  27. (1994). Cometary Lander of the Rosetta Mission. Preliminary proposal to ESA. RoLand consortium,
  28. (1971). Comments on the Moving-Source Soil Density Gauge. doi
  29. (1997). Cone Penetration Testing in Geotechnical Practice. doi
  30. (1989). Course to Mars. Mashinostronie,
  31. (1989). Crustal Strength of Different Model Comet Materials.
  32. (1994). Densities of Stratospheric Micrometeorites. doi
  33. (1997). Densitometer Instrument of MUPUS– Design Thoughts.
  34. (1960). Density Logging. doi
  35. (1994). Density of Comet Shoemaker-Levy 9 Deduced by Modelling Breakup of the Parent ‘Rubble Pile’. doi
  36. (1992). Depth of Investigation of Density Tools. doi
  37. (1997). Depth Prediction for Earth-Penetrating Projectiles.
  38. (1996). Design and Performance of a Moving Gamma-Source Soil Density Gauge. doi
  39. (1995). Development of a Method for Hardness and Cohesivity Measurements on Cometary Surface Layers Using a Harpoon Device: Progress Report I.
  40. (1990). Dynamical Aspect of Lunar Penetrator. doi
  41. (1957). Dynamics of a Projectile Penetrating Sand. doi
  42. (1996). Emplacement of Penetrators into Planetary Surfaces. doi
  43. (1996). Energy Loss and Sticking Mechanisms in Particle Aggregation in Planetesimal Formation. doi
  44. (1994). ESA’s Planetary Cornerstone Mission.
  45. (1993). Evolution of a Porous H2O - CO2 - Ice Sample in Response to Irradiation. doi
  46. (1990). From the Moon Rover to the Mars Rover. The Planetary Report X(4),
  47. (1975). Gamma-Gamma Method of Investigation of Oil Wells. doi
  48. (1977). Gamma-Ray Absorption Coefficient for Non-Homogeneous Materials. doi
  49. (1990). Gas Release in doi
  50. (1977). Geochemical studies of Venus by Venera 9 and 10 automatic interplanetary stations.
  51. (1986). Geophysical Well Logging. doi
  52. (1942). High Resolution Tomography of Objects with Access to a Single Side. doi
  53. (1942). High Resolution Tomography of Objects with Access to a Single Side. In Underground and Obscured Object Imaging and Detection, doi
  54. (1962). Impact Characteristics of Various Materials Obtained by an Acceleration-Time-History Technique Applicable to Evaluating Remote Targets.
  55. (1982). In situ Density-Measurement in Aqueous Solutions by the Gamma-Ray Backscattering Method. doi
  56. (1990). In: Physics and Chemistry of comets. doi
  57. (1995). Influence of the Vapor Flux on Temperature, Density, and Abundance Distributions in a Multicomponent, Porous, Icy Body. doi
  58. (1977). Investigations of the Density of the Venusian Surface Rocks by Venera 10. Space Res.
  59. (1988). Is the Nucleus of Comet Halley a Low Density Body? doi
  60. (1997). Laboratory Development of the MUPUS Densitometer for the Rosetta Comet Lander. Poster PS076 at the European Geophysical Society,
  61. (1991). Laboratory Simulation, a Tool for Comet Research. doi
  62. (1992). Laborexperimente und Modellrechnungen zur Untersuchung der thermischen Evolution poröser Eis-Staub-Proben unter Weltraumbedingungen: Konsequenzen für Kometen und andere planetare Eiskörper.
  63. (1996). Local Densitometry of Wood by Gamma BackScattering. Holz als Roh- doi
  64. (1985). Logging- A 25-Year Perspective. doi
  65. (1997). Low Velocity Projectile Penetration. doi
  66. (1995). Lunar Interior Exploration by Japanese Lunar Penetrator Mission, doi
  67. (1991). Lunar Sourcebook: A User’s Guide to the Moon. doi
  68. (1994). Meteoroid Streams as Probes of the Subsurface Regions of Comets. doi
  69. (1990). Microwave Dielectric Properties of Dry Rocks. doi
  70. (1996). Modeling the Thermal Properties and the Gas Flux from a Porous, Ice-Dust Body in the Orbit of P/Wirtanen. doi
  71. (1986). Modelling gamma-source backscatter density gauges. doi
  72. (1996). Models of the Structure and Evolution of Comet P/Wirtanen. doi
  73. (1976). Monte Carlo Principles and Applications. doi
  74. (1996). MUPUS - a suite of small instruments for the RoLand Comet Lander to study thermal and mechanical properties. Presented at COSPAR
  75. (1998). MUPUS-TM: IR-Measurement of Comet P/Wirtanen’s Surface Temperature. Presented at the European Geophysical Society,
  76. (1995). NDT Using Compton Scattering. doi
  77. On the Density of Halley’s Comet. doi
  78. (1993). On the Determination of the Effective Volume of a Gamma Ray Density Gauge in Backscatter Mode.
  79. (1981). On the Electrostatic Charging of the Cometary Nucleus. doi
  80. (1995). On the Stability of Dust Particle Orbits Around Cometary Nuclei. doi
  81. (1995). Orbit Perturbations in the Vicinity of an Active Cometary Nucleus. doi
  82. (1992). Penetration into Soil Targets. doi
  83. (1970). Photon Cross Sections from 1 keV to 100 doi
  84. (1997). Physical Risks of Landing on a Cometary Nucleus. doi
  85. (1990). Physics and Chemistry of Comets. doi
  86. (1995). Physics and Chemistry of the Solar System. doi
  87. (1971). Portable Gauges for Radiometric Determination of the Density and Moisture Content of Building Materials. doi
  88. (1989). Principles of Dielectrics.
  89. (1996). Production and Chemical Analysis of Cometary Ice Tholins.
  90. (1992). Prospects for Using Mobile Vehicles in Missions to Mars and Other Planets.
  91. (1988). Ray Scattering Measurements for Density and Lithology Determination. doi
  92. (1994). Recent Progress in Single Sided Gamma-Ray Tomography. In Aerial Surveillance Sensing Including Obscured and Underground Object Detection, doi
  93. (1995). Responsible Proposer: Prof. Tilman Spohn, Institut für Planetologie, Westfälische Wilhelms-Universität,
  94. (1990). RoLand Cometary Lander of the Rosetta Mission. Preliminary proposal to ESA. RoLand consortium,
  95. (1989). Rosetta/CNSR– ESA’s Planetary Cornerstone Mission.
  96. (1989). Scattered X-Ray Beam Nondestructive Testing. doi
  97. (1995). Simultaneous Estimation of the Masses of Mars, Phobos and Deimos using Spacecraft Distant Encounters. doi
  98. (1942). Single Sided Tomography of Extremely Large Dense Objects. doi
  99. (1969). Soil Mechanics Surface Sampler. doi
  100. (1987). Solar System Log.
  101. (1989). Some Considerations on Cohesive Forces in Sun-Grazing Comets.
  102. (1992). Soviet Developments of Planet Rovers in Period of 1964-1990. doi
  103. (1990). Surface Features and Activity of the Nucleus of Comet Halley. doi
  104. (1977). Surface Materials of the Viking Landing Sites. doi
  105. (1994). Surface Regolith and Environment of Comets. doi
  106. (1972). Terminal ballistics in ordinary snow.
  107. (1991). The Accumulation and Structure of Comets. doi
  108. (1987). The Comet Rendezvous Asteroid Flyby Mission: A Search for Our Beginnings. doi
  109. (1993). The Discovery and Orbit of doi
  110. (1968). The Dusty Gas Dynamics of Comet Heads.
  111. (1990). The Formation and Structure of Fluffy Cometary Nuclei from Random Accumulation of Grains.
  112. (1994). The Formation of Cometary Surface Crusts. doi
  113. (1990). The influence of CO ice on the activity and near-surface differentiation of comet nuclei. doi
  114. (1996). The Interior of a Cometary Nucleus. doi
  115. (1998). The International Rosetta Mission. doi
  116. (1995). The McLDL Code with Subspace Weight Window-biasing Combined with the Monte Carlo Multiply Scattered Components Approach for Simulation of Gamma-Gamma Litho-density Logging Tools. doi
  117. (1997). The Mobile Penetrometer, a “Mole” for Sub-surface Soil Investigation. doi
  118. (1996). The New Russian Space Programme. doi
  119. (1983). The Physical Foundation of Formation Lithology Logging with Gamma Rays. doi
  120. (1965). The Physical Foundations of Formation Density Logging (Gamma-Gamma). doi
  121. (1962). The Physics and Mechanics of Snow as a Material.
  122. (1998). The Response of Gamma Backscatter Density Gauges to Spatial Inhomogeneity– doi
  123. (1996). The Response of Gamma Backscatter Density Gauges to Spatial Inhomogeneity– an Extension of the Single Scattering Model. doi
  124. (1969). The RIDS: a Density Logger for Rough Holes. doi
  125. (1996). The Shape of Ida.
  126. (1970). The Spatial Response Pattern of Gamma Backscatter Density Gauges. doi
  127. (1991). Thermal budget of Multicomponent Porous Ices. doi
  128. (1996). Thermal Properties of Cometary Ices and Sublimation Residua Including Organics. doi
  129. (1994). Tidal Disruption of Periodic Comet Shoemaker-Levy 9 and a Constraint on its Mean Density. doi
  130. (1954). Tube Wall Thickness Gauge with Selection of Backscattered Gamma Radiations. doi
  131. (1929). Über die Streuung von Strahlung durch freie Elektronen nach der neuen relativistischen Quantendynamik von Dirac. doi
  132. (1992). Untersuchung der Festigkeit Poröser Eis-Mineral-Körper Kometarer Zusammensetzung. Diploma Thesis,
  133. (1997). Using the Anchoring Device of a Comet Lander to Determine Surface Mechanical Properties. doi
  134. (1991). Wanderers in Space: Exploration and Discovery in the Solar System. doi
  135. (1987). Well Logging for Earth Scientists. doi

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